1. Field of the Invention
The present invention relates to a powder discharging device including a powder container formed with an outlet for discharging powder and shock applying means for applying a shock to the toner container, and an image forming apparatus using the same.
2. Description of the Background Art
It is a common practice with a copier, facsimile apparatus, printer or similar image forming apparatus to use a toner container storing toner or powder for image formation. For example, in an electrophotographic image forming apparatus configured to form a latent image on an image carrier and then develop it with a developing device, toner is replenished from a toner container to the developing device, as needed. This is also true with a direct recording type of image forming apparatus that causes toner to fly from a toner jetting device toward a sheet or similar recording medium in the form of dots. The toner container is constructed integrally with the developing device or the toner jetting device or implemented as a toner cartridge removably mounted to the apparatus body. When a toner cartridge, for example, mounted to the apparatus body becomes almost empty, it is replaced with a new toner cartridge. At this instant, the toner, if left in the toner cartridge in a large amount, would be wastefully discarded and increase the running cost of the apparatus and would bring about an environmental problem. It is therefore desirable to minimize the amount of toner to be left in the used toner cartridge.
Japanese Patent Laid-Open Publication No. 2002-46843, for example, discloses atoner cartridge configured to discharge toner without wasting it as a toner discharging device. The toner discharging device taught in this document includes a toner cartridge formed with an outlet in its bottom for discharging toner or powder and shock applying means for applying a shock to the toner cartridge. When the shock applying means applies a shock to the toner cartridge, the toner present in the toner cartridge is moved toward the outlet of the toner cartridge and then discharged via the outlet. In this configuration, the toner can be discharged without any waste despite that the toner cartridge lacks a movable member.
However, the toner discharging device with the shock applying means has the following problems left unsolved. When the toner is left unused over a long period of time or used in, e.g., a hot, humid environment, the fluidity of the toner decreases with the result that the amount of the toner to be discharged via the outlet formed in the toner cartridge decreases, resulting in short toner replenishment. To solve this problem, it is necessary to set a relatively large amount of toner discharge beforehand.
The amount of toner discharge may be effectively increased if the shock to act on the toner cartridge is intensified. However, if the shock is excessively intense, then the toner coheres due to compression in the outlet of the toner container and stops it up, i.e., so-called toner blocking occurs. Further, an excessive shock is apt to cause the resulting vibration to be imparted to the apparatus body, adversely effecting an image. If the shock is limited to a degree that does not effect an image, then it is likely that the discharge of the toner cannot follow the consumption of the same when an image with a relatively large area ratio is continuously output.
The toner may be stably discharged from the toner cartridge without regard to the intensity of the shock if the outlet of the toner container is increased in size. This, however, brings about smearing ascribable to the toner in the event of mounting or dismounting of the toner cartridge to or from the apparatus body.
The problems described above are apt to occur even when the toner is replaced with a pigment or similar powder.
On the other hand, Japanese Patent Laid-Open Publication 2002-96882 proposes a powder discharging device constructed to cause a powder container to reciprocate such that an inertia force acts on powder stored in the powder container, thereby discharging the powder. The powder container is formed with an outlet in one end portion of one side wall. Reciprocating means causes the powder container, which is positioned such that the outlet is oriented vertically downward, to reciprocate to thereby move the powder toward the outlet little by little. The powder, reached the outlet, drops via the outlet due to gravity. This configuration makes it needless to arrange a spiral lug, groove or similar special structure or a screw or similar movable member in the powder container and therefore allows the powder to be surely discharged by a simple, low-cost structure.
Further, in the reciprocation type of powder discharging device stated above, an acceleration to act on the powder container when the powder container, moving forward with respect to the direction in which the powder moves toward the outlet, is caused to stop is sized greater than an acceleration to act when it is caused to stop after backward movement, and is so sized as to allow the powder to bodily move toward the outlet. Consequently, an inertia force to act on the powder in the forward direction on the stop of the toner container after forward movement is greater than an inertia force to act on the same in the backward direction on the stop of the toner container after backward movement. The powder can therefore be moved toward the outlet by the reciprocation of the powder container. Moreover, because the acceleration generated by the stop after forward movement is so sized as to allow the powder to bodily move toward the outlet, i.e., 40 m/sec2 or above, the powder can be moved toward the outlet without remaining at the side opposite to the outlet.
Laid-Open Publication No. 2002-96882 stated above describes that by limiting the maximum acceleration to act on the powder container when the powder container is stopped after forward movement to 200 m/sec2, it is possible to replenish the powder by a stable amount without causing it to cohere around the outlet. We, however, experimentally found that when the acceleration at the time when the toner container is stopped after forward movement is simply selected to be 40 m/sec2 or above, the amount of the powder discharged via the outlet is sometimes short. This is also true with, e.g., a powder discharging device configured to suddenly reverse the movement of a powder container moving forward.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Utility Model Laid-Open Publication No. 2-134554 and Japanese Patent Laid-Open Publication Nos. 9-244372, 2000-81723, 2001-34008, 2002-6533, 2002-72645, 2002-99136, 2002-182461 and 2002-268346.